The present invention relates generally to the field of image signal processing, and more particularly to calibration techniques for use in video conferencing and other camera-based system applications.
In conventional video conferencing systems and other known camera-based systems, it may be desirable to determine, using image signal processing techniques, a direction in which a particular participant is pointing. For example, such a participant may be pointing at a white board or other presentation display, an object, or another local participant. In these and other cases the system can use the direction of pointing to bring the pointed-to display, object or participant into the field of view of a camera so as to be visible to remote participants.
A problem associated with the determination of pointing direction in video conferencing and other applications is that different people may have different ways of pointing. For example, some people may point in such a way that the direction of the user""s arm will intersect with a desired target point. Others, however, may point using primarily a finger and a reference point such as a right or left eye. In the latter case, the direction of the arm may be insufficient to determine accurately where the person is pointing. Using the same model to characterize the pointing mechanism of all users can therefore introduce inaccuracies in the determination of pointing direction.
An example of a conventional camera-based system that involves determination of user pointing direction is described in European Patent Application No. EP 913790 A1, published May 6, 1999 and entitled xe2x80x9cHand Pointing Apparatus.xe2x80x9d This system processes images obtained from a set of video cameras oriented in different directions in order to determine a particular portion of a virtual three-dimensional space that is being pointing to by a user. However, this system and other similar conventional systems fail to provide a calibration technique for determining the manner in which a given user points. The system thus suffers from the above-noted inaccuracies that can arise when an assumption is made that all users point in the same manner.
It is therefore apparent that a need exists for a calibration technique that can determine the particular manner in which an individual user points, such that when that user is pointing at a display, an object or another user, the system can more accurately determine the pointing direction.
The invention provides a calibration technique that can be used to determine calibration information characterizing the manner in which an individual user points within a camera-based system. The resulting calibration information is used in a subsequent pointing direction determination, and ensures that the pointing direction determination is more accurate than would otherwise be possible without the calibration.
In accordance with the invention, a camera-based system directs the user to point separately at each point in a set of two or more points at different positions on a display. The points may be in the form of icons that are displayed sequentially or simultaneously at different positions on the display. The system then detects, for each of the points pointed to by the user, a location of a pointing finger of the user in an image generated by each camera in a set of cameras of the system, such that for each of the points the location of the pointing finger and the corresponding point on the display specify a line. The lines associated with the points are then used to compute a reference point or other pointing direction calibration information for the user. For example, the reference point may be determined as an intersection of the computed lines. The calibration information for the user may be stored with user-identifying information in a database of the system, and is utilized in subsequent pointing direction determinations for that user.
In an illustrative embodiment, the system includes at least two cameras, and determines the location of the pointing finger of the user in both an image generated by a first camera and an image generated by a second camera.
The techniques of the invention can be used in a wide variety of image processing applications, including camera-based systems such as video conferencing systems, video surveillance and monitoring systems, and human-machine interfaces. These and other features and advantages of the present invention will become more apparent from the accompanying drawings and the following detailed description.